The invention relates generally to air conditioning and refrigeration systems, and more specifically to a refrigeration system having a cooling mode, a heating mode, and a defrost mode and a method of operating the refrigeration system in the cooling, heating, and defrost modes.
Conventional refrigeration systems are commonly used-to maintain the temperature of an air-conditioned space at or near a set point temperature and typically include a compressor, a condenser, an expansion valve, and an evaporator. Generally, refrigeration systems operate in cooling, heating, and defrost modes, depending, at least in part, upon the temperature of the air-conditioned space and the ambient temperature outside the air-conditioned space. When the temperature of the air-conditioned space is above the set point temperature, the refrigeration systems operate in the cooling mode to pull down the temperature in the air-conditioned space. During operation in the cooling mode, refrigerant is directed along a refrigerant circuit, which includes the condenser, a receiver tank, the expansion valve, the evaporator, and an accumulator tank.
When the temperature of the air conditioned space is below the set point temperature, the refrigeration systems operate in a heating mode. Additionally, to minimize the formation of ice and frost on the evaporator coil and to ensure that the refrigeration system is operating in the most efficient manner, refrigeration systems periodically operate in a defrost mode. When the system is switched from the cooling mode to the heating or defrost modes, hot refrigerant vapor is directed out of the compressor through a heating circuit, which includes a pan heater, the evaporator and the accumulator tank.
The heating and defrosting capacity of the system depends, at least in part, upon the volume of refrigerant being directed through the heating circuit. Therefore, it is desirable to ensure that a maximum amount of refrigerant is directed through the heating circuit during heating and defrost modes. Moreover, during heating and defrost modes, refrigerant which has accumulated in the condenser is unavailable for heating and defrosting. Therefore, it is desirable to ensure that refrigerant does not accumulate in condenser during heating and defrost modes.
According to the present invention, a transportation refrigeration system operable in a cooling mode, a defrost mode, and a heating mode to condition air in an air-conditioned space comprises a refrigeration circuit fluidly connecting a compressor, a condenser, a tank, and an evaporator. The evaporator is in thermal communication with the air-conditioned space. The system further comprises a heating circuit fluidly connecting the compressor, the tank, the evaporator, and a heater. The system also comprises a defrost circuit fluidly connecting the compressor, the tank, the evaporator, and the heater.
In some embodiments of the transportation refrigeration system, a substantial quantity of a refrigerant is directed through the refrigeration circuit during operation in the cooling mode. The substantial quantity of the refrigerant is also directed through the heating circuit during operation in the heating mode and the defrost mode.
The transportation refrigeration system includes a controller operable to selectively direct a quantity of a refrigerant through the refrigeration circuit, the defrosting circuit, and the heating circuit during operation in the cooling mode, the defrost mode, and the heating mode, respectively. A plurality of adjustable valves are distributed throughout the refrigeration system and are operable to selectively alter the flow of refrigerant through the refrigeration circuit, the heating circuit, and the defrost circuit.
The tank includes a first opening, a second opening, and a third opening. The refrigeration circuit is coupled to the first and second openings. The heating circuit is coupled to the first and third openings, and the defrost circuit is coupled to the first and third openings. The tank includes a base and the first opening is spaced a first distance above the base and the third opening is spaced a second smaller distance above the base. A quantity of oil is periodically mixed with the refrigerant in the compressor and the tank periodically separates at least some of the oil from the refrigerant.
Also according to the present invention, a method of conditioning air in an air-conditioned space with a transportation refrigeration system having a refrigerant comprises directing substantially all of the refrigerant through a refrigeration circuit during operation in a cooling mode. The refrigeration circuit includes a tank and an evaporator. The evaporator is in thermal communication with the air-conditioned space. The method further comprises directing substantially all of the refrigerant through a heating circuit during operation in a heating mode. The heating circuit includes the tank, the evaporator coil, and a heater. The method also includes directing substantially all of the refrigerant through a defrost circuit during operation in a defrost mode. The defrost circuit extends through the tank, the heater, and the evaporator.
In some embodiments, the refrigeration circuit includes a condenser and the method includes removing at least a substantial quantity of refrigerant from the condenser before initiating the defrost mode.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.